A number of existing wireless sensing and control systems employ narrowband communication techniques to remotely control devices such as garage doors and car alarms. Unfortunately, simple narrowband systems are relatively susceptible to unintentional jamming by spurious and intermittent electromagnetic emissions from other common electronic devices such as computers, medical equipment, and household appliances, rendering them unreliable. In this regard, narrowband or single frequency receivers may be overwhelmed by the ambient noise level, preventing them from receiving the intended transmission.
One known system utilizes an RF carrier that is sequentially modulated at two different audio frequencies to prevent unauthorized control of a garage door opener. Another known remote transmitter device uses multiple RF carrier frequencies in a predetermined sequence to prevent unauthorized control of the destination device. These conventional remote control or sensor transmitter devices do not use multiple frequencies to improve the reliability of receiving the correct signal (or data) in the presence of unintentional interference from other electronic devices. In contrast, such devices employ multiple audio or radio frequencies to improve the security of the system and to prevent unauthorized control.
In the fields of wireless computer and telecommunication systems, spread spectrum systems using direct sequence and frequency hopping have been used to prevent unauthorized interception of the transmitted signal and immunity to intentional jamming. Spread spectrum communication systems spread the information over a wide bandwidth to achieve resistance to interception and intentional jamming of narrowband transmit frequencies. Typical spread spectrum system spread the transmitted signal over a bandwidth that is at least ten times that of the original base-band signal.
While very effective at achieving their intended objectives, existing spread spectrum systems have certain drawbacks. For example, because the transmitted signal is spread over a wide bandwidth, the transmitter and receiver must have an accurately synchronized de-spreading mechanism that is inherently more complex and dissipates more power than the simpler narrowband transmitters and receivers that are typically used for remote control devices. The complicated nature of conventional spread spectrum designs and the associated high power requirements make these designs undesirable for many applications that mandate inexpensive and efficient remote transmitter devices.
The prior art lacks a reliable wireless remote control and sensor system that is relatively immune to unintentional interference from other electronic devices, requires very little operating power, and can be implemented using cost-effective design techniques.